FIG. 4 and FIG. 5 show a general and conventional cement plant. The cement plant includes a cement kiln 1 for burning cement raw material, a preheater 4 including a plurality of cyclones 4a to 4d provided toward a kiln inlet part 2 of the cement kiln 1, a chute 5 which feeds the cement raw material to the kiln inlet part 2 of the cement kiln 1 from the cyclone 4d of the preheater 4 in its lowermost stage, an exhaust line 7 connected to the cyclone 4a in the uppermost stage and having an exhaust fan 6 which discharges combustion exhaust gas, and a main burner 8 provided at a kiln outlet part 3 for heating the inside of the cement kiln 1, and further includes a calciner 10, between the cyclone 4c in the third stage and the cyclone 4d in the fourth stage, to the lower end part of which exhaust gas at high temperature is introduced from the kiln inlet part 2 of the cement kiln 1 through an exhaust gas pipe 9 and inside of which a combustion apparatus of fine powder carbon is provided.
Furthermore, in the above-mentioned plant of cement clinker, the above-mentioned cement raw material fed to the cyclone 4a in the uppermost stage is preheated by the exhaust gas at high temperature from the cement kiln 1 which gas elevates from the downside as the cement raw material falls downward sequentially in the cyclone 4; after that, is pulled out from the cyclone 4c to be sent to the calciner 10 and is calcined in the calciner 10; after that, is introduced to the kiln inlet part 2 of the cement kiln 1 from the cyclone 4d in the lowermost stage through the chute 5; and is sent from the kiln inlet part 2 side to the kiln outlet part 3 in the cement kiln 1 which is driven to rotate around its axis line, being burnt to afford cement clinker in this process.
Meanwhile, combustion exhaust gas discharged from the cement kiln 1 is configured to be mixed with exhaust gas from the calciner 10 in the exhaust gas pipe 9; after that to be sent to the cyclone 4d in the lowermost stage and to be sent to the upside sequentially in the cyclone 4; and to preheat the above-mentioned cement raw material and to be finally discharged by the exhaust fan 6 from the upper part of the cyclone 4a in the uppermost stage through the exhaust line 7.
In such a cement plant, a chlorine component contained in the cement raw material and/or a chlorine component contained in waste such as plastics which is thrown in as a part of fuel are evaporated mainly as alkaline chloride such as KCl and NaCl under an atmosphere at a high temperature (approximately 1400° C.) in the cement kiln 1 to transfer into the exhaust gas. Then, when being discharged from the kiln inlet part 2 of the cement kiln 1 to the preheater 4 side and elevating sequentially in the cyclones 4d to 4a from the downside to the upside, the exhaust gas is cooled by preheating the cement raw material, and the chlorine component contained in the relevant exhaust gas results in its transfer again to the cement raw material side.
As a result, since the chlorine component cycles in the system constituted of the above-mentioned cement kiln 1 and preheater 4, due to a chlorine component or the like newly brought in the system from the above-mentioned fuel or cement raw material, the chlorine concentration inside elevates gradually, and eventually, causes occlusion of the cyclones of the preheater 4 and deficiently affects the operation.
Therefore, in a cement plant as mentioned above, a chlorine bypass apparatus for removing a chlorine component in the system is provided in recent years. The chlorine bypass apparatus is schematically configured of a gas extracting pipe 11 which is connected to the exhaust gas pipe 9 from the kiln inlet part 2 and picks out and cools a part of the exhaust gas, a cyclone 12 which separates and removes cement raw material that is large in particle diameter from the exhaust gas picked out by the gas extracting pipe 11, and a bag filter 13 which catches the chlorine component contained in the exhaust gas having passed through the cyclone 12.
According to the above-mentioned chlorine bypass apparatus, a part of exhaust gas discharged from the cement kiln 1 through the exhaust gas pipe 9 is periodically picked out and cooled by means of the gas extracting pipe 11 to thereby recover the chlorine component as alkaline chloride in the downstream bag filter 13, and thus the chlorine concentration in the system can be prevented from elevating.
As shown in FIG. 5, in a cement plant generally having the above-mentioned configuration, in order to feed, as a heat source to the upside preheater 4, the exhaust gas that is discharged from the kiln inlet part 2 of the cement kiln 1 whose axis line is substantially horizontal, the exhaust gas pipe 9 connected to the kiln inlet part 2 of the cement kiln 1 is formed of a pipe inclination part 14 gradually inclining upward toward the downstream side of a kiln exhaust gas (A) from the relevant kiln inlet part 2, and a rising duct (vertical part) 15 which is connected to the upper end part of the pipe inclination part 14 and introduces the exhaust gas (A) to the preheater 4.
Furthermore, an exhaust duct 16 of the calciner 10 is connected to the upside face of the pipe inclination part 14, and in addition, the gas extracting pipe 11 of the chlorine bypass apparatus is connected to the upside face of the pipe inclination part 14 between the exhaust duct 16 and the kiln inlet part 2. The exhaust duct 16 from the calciner 10 is commonly provided so as to be located as close to the kiln inlet part 2 side as possible such that heat exchange is efficiently performed between the exhaust gas (A) from the cement kiln 1 and dusts of the raw material along with calciner exhaust gas (B).
As a result, as indicated by a dot and dash line in the figure, there arises a phenomenon in which a part of the calciner exhaust gas (B) discharged from the exhaust duct 16 falls toward the kiln inlet part 2 side and is picked out along with a part of the kiln exhaust gas (A) from the gas extracting pipe 11 of the chlorine bypass apparatus (see analysis results shown in FIG. 6).
Here, although the chlorine bypass apparatus is designed on the assumption that the kiln exhaust gas (A) as high in concentration of the chloride gas as possible is extracted by a small amount, since the above-mentioned calciner exhaust gas (B) is low in concentration of the chloride gas compared with the kiln exhaust gas (A), the practical operation consequently results in picking-out of the exhaust gas whose concentration of the chloride gas is diluted with the calciner exhaust gas (B) from the gas extracting pipe 11.
As a result, there has been a problem that it is difficult to reduce the concentration of the chloride gas in the cement kiln 1 as specified in the design and specifications. When, on the other hand, in order to attain a predetermined reduction effect of the concentration of the chloride gas in the cement kiln 1 by increasing an amount of chlorine removal in the chlorine bypass apparatus, an amount of the exhaust gas extracted by the gas extracting pipe 11 is increased, there has been a problem that heat loss in the system becomes too much, causing manufacturing costs of the clinker to increase and productivity to deteriorate.
In addition, as a conventional cement plant including this kind of calciner and chlorine bypass apparatus, for example, ones which Patent Literatures 1 and 2 disclose as follows are known.